Automatic volume control



sept. 6, 1938.

M. G. NICHOLSON, JR

AUTOMATIC VOLUME CONTROL Filed NOV. 25, 1931 2 Sheets-Sheet l TETE 7'0 @UTPL/7' TUBE INVENTOR ATTORNEY Sept. 6, 1938. l M. G. NICHOLSON, JR Y 2,129?021 AUTOMATIC VOLUME CONTROL W ATTORN EY Patented Sept. 6, 1938 UNITED STATES PATENT OFFICE AUTOMATIC VOLUME CONTROL tion of Delaware Application November 25, 1931, Serial No.577,235

15 Claims.

'Ihis invention relates to automatic volume control in radio receiving sets, and more particularly is directed to the elimination of noise encountered in tuning from one station to another.

In present day receiving sets it is common practice to obtain automatic volume control through automatic control of the radio frequency amplier. This form of control has two serious disadvantages, namely, noise is encountered in tuning from one station to another and exact tuning is difficult unless a tuning meter is used.

It is an object of my invention to provide an automatic volume control circuit arrangement which eliminates noise when tuning between stations.

It is another object to provide a circuit organization in which automatic volume control may be successfully applied Without using a tuning meter.

Another object of the invention is the provision of a circuit organization in which certain instrumentalites thereof are so connected as to block signals below a certain level, which level might be adjusted to pass only signals `strong enough to be relatively free from noise disturbances.

To avoid the above mentioned difficulties and accomplish the objects of the invention I propose to exercise control over the output of the audio frequency amplier through a controlling circuit actuated by the output of the radio frequency amplifier.

In the accompanying drawings:

Fig. 1 represents very schematicallythe general circuit arrangement of present day automatic volume control having associated therewith my auxiliary circuit for effecting automatic volume control of the audio frequency amplifier.

Fig. 2 represents schematically my invention reduced to its simplest form. Y

Fig. 3 is a modification of the circuit arrangement shown in Fig. 2, this modification making the control contemplated more positive.

Fig. 4 illustrates schematically the invention embodied in a commercial form ofsuperheterodyne.

Fig. 5 represents another application of my invention of a circuit employing diode type detection; and a Fig. 6 is a circuit arrangement whereby compensation is obtained in cases of inadequatecontrol of the radio frequency automatic .volume control.

To obtain a general understanding of the invention before proceeding to describe inndetail the various circuit arrangements, reference may be had to Fig. l. I have shown therein, by the block diagram method, the incoming signal being received by the radio frequency amplier. The output of the radio frequency amplifier divides into two circuits, one of which actuates the radio frequency automatic volume control and the other the detector. From the detector the output feeds the audio frequency amplifier and thence to the loud speaker. By this circuit arrangement noises occurring between stations and the like would be heard in the loud speaker when tuning from one station to another.

By the introduction of a special automatic controlling circuit I largely overcome or eliminate these noises entirely, depending upon the selectivity or non-selectivity of such controlling circuit. This controlling circuit is actuated by the output of the radio frequency amplier and controls the audio frequency amplifier output. shown in Fig. l the controlling circuit may have inserted therein any satisfactory form of selective circuit such as a loosely coupled highly selective resonant circuit.

Referring to Fig. 2, which is intended to illustrate my invention reduced to its simplest form, it will be seen `my controlling circuit may comprise using the detector tube as both the detector Asl , and the audio frequency automaticl volume control. Only such part of the apparatus is shown in this and other circuits as is necessary to appreciate the working of the circuit. In this instance the incoming signal comes from the plate of the last radio frequency amplifying tube (which may be in any conventional circuit) and is received by the detector. The received signal in the detector causes an increase in the cathode current, thereby raising its potential in the positive direction. This potential is applied through an appropriate circuit (either resistive or inductive), as grid bias to the rst audio frequency amplifier which has been biased negatively to or beyond the cut-off. It is seen that if the potential of the cathode of the detector is raised sufliciently in the positive direction the audio frequency amplier becomes operative. By suitable adjustment and a selection of suitable resistances and potentials the circuit will be inoperative except for signals above a certain value. The desired value is one just above the existing noise level for a given location. As indicative of what might be satisfactory voltages for the 227 type tubes I have given certain voltages but it is understood that the same will vary with choice of resistances, tubes, etc.

Referring to Fig. 3 there is shown a modification of the circuit arrangement of Fig. 2 Which gives a controlling action of larger magnitude by the insertion of a Vacuum tube (V. T. l) used as a constant current amplifier. This changing cathode potential actuates the constant current amplifier which in turn supplies the controlling grid bias for the audio frequency amplifier. As in Fig. 2 I have merely indicated potentials which may be used with the 227 type tube.

Fig. 4 is only that part of a standard superheterodyne circuit which is required to illustrate my auxiliary controlling circuit as applied thereto. In this circuit organization a highly selective circuit is inserted between the source of radio frequency voltage and the audio frequency automatic volume control tube. 'Ihe selective circuit may comprise the usual parallel resonant circuit loosely coupled to the radio frequency voltage source. It is to be appreciated that the radio frequency voltage is theincoming signal Whether it be a broadcasting'station or noise.` The rst audio frequency amplifier tube is biased beyond the cut-off, thereby making it inoperative until a signal of sufficient magnitude is applied to the audio frequency automatic volume control tube which makes it operative by virtue of reducing its grid bias to normal. In this circuit a constant current amplifier is used to aid and stabilize this controlling action.

It is appreciated that the signal reaching the audio frequency automatic volume control Will only be one which can pass through the highly selective circuit. Therefore, the audio f requency amplifier is operative only when the signal of the radio frequency is supplied to the highly selective circuit from the radio frequency (in this instance intermediate frequency) amplifier. If a broad band of frequencies (noise) is applied to the highly selective circuit only a small percentage of said frequencies will be passed through to the audio frequency automatic volume control tube. The audio frequency volume control tube is so adjusted that this small amount of radio frequency voltage does not actuate it but a signal of suiiicient magnitude and of the right frequency will actuate said control tube.

That is to say, if the receiving set to which the above is applied has a radio frequencyautomatic volume control that holds the radio frequency level reaching the added selective circuit reasonably constant, and this circuit is selective enough, the set Will be silent except when a station is properly tuned in. The set is insensitive to noise, since the added selective circuit is not sensitive to a band of frequencies (noise), but only to a constant frequency of the right frequency, i. e., the carrier wave of a properly tuned in station. If the signal being received fades to such a point Where the ratio of noise to a signal is greater than a certain amount (depending upon selectivity of added tuned circuit, etc), the receiving set automatically becomes silent until the strength of the signal increases to the necessary amount above that of the noise. The above holds true when tuning in Weak stations. Only the ones Which are sufficiently strong above the existing noise Will be received, the receiving set being silent at all other times.

The circuit shown in Fig. 5 is a modification of the one shown in Fig. 4, the essential difference being that the detection is accomplished by the so-called diode detector method. The same tube is also used to feed a highly selective circuit which in turn supplies the audio frequency automatic volume control tube. The diode detector action occurs between the cathode and the control grid of this tube (tetrode) While the screen grid and. plate serve as amplifier for the radio frequency voltage to be applied to the audio frequency automatic volume control tube. In addition to supplying large voltages this circuit also has the advantage of additional automatic control of the magnitude of the voltage applied to vthe audio frequency automatic volume control tube. This is true because for an increase of the radio frequency voltage to the detector grid, the output voltage to the audio frequency automatic volume control tube will not be increased proportionately, since the diode action of the detector causes ,an increase in the effective negative grid bias of the tetrode relative to its use as a radio frequency amplifier.

In each of the circuit arrangements shown in Figs. 4 and 5 I have indicated certain voltages which, as intimated above, Will depend upon the electrical characteristics `of the tubes used in the circuit and the values of the resistances' used. With the notations or legends used in the drawings it is believed that these circuits are sufflciently clear to those skilled in the art as not to require reference characters to designate the various electrical devices which are employed inasmuch as they are conventionally represented and their functions Well understood.

Referring to the circuit arrangement illustrated very schematically in Fig. 6, it will be noted that the same is a modification of the circuits represented particularly by Figs. 4 and 5. A special feature of this circuit is the compensation system for compensating when receiving strong signals Which the radio frequency automatic volume control does not adequately control or keep down to a certain level arbitrarily established. The operation of the compensation circuit is to increase the bias voltage on the audio frequency automatic volume control tube as the applied signal to the audio frequency automatic volume control tube increases by virtue of the fact that the radio frequency automatic Volume control tube does not precisely hold the radio frequency level to a constant or established value.

The compensating circuit in short may be regarded as a refinement of the audio automatic volume control circuit shown in Figs. 4 and 5 and has for its principal function to bring about smoother action or control of extremely strong signals.

Various modifications of the invention Will suggest themselves to those skilled in the art. As for example the highly selective coupling circuit for supplying the voltage to the audio frequency automatic Volume control tube may be modified to give greater or less selectivity depending upon the type of set to which the invention is applied. `The method of coupling the output of the radio frequency amplier to the highly selective circuit may also be varied.

Another modification which suggests itself Would be to control the output of the audio frequency amplifier by means of a relay, rather than to control the input or gain of the audio frequency amplifier by biasing one of the audio frequency amplifier tubes to cut-off, as described above.

Such modifications are obvious from a proper appreciation of my invention, which in its broadest aspects contemplates automatic volume control through a circuit arrangement Which is adapted to effectively interrupt the audio circuits of aV receiving system at any point between the detector and therloud speaker. It is my intention to cover all such modifications as come within the scope of the appended claims.

What is claimed is:

1. In a radio receiving set, a radio frequency amplifying system, a detector tube, an audio frequency amplifying system, means for automatically controlling the volume of the signal output of the radio frequency amplifier, means for automatically controlling the volume of the signal output of the audio frequency amplifier in such a manner that its sensitivity is a minimum when signals below a predetermined intensity level are received, said last mentioned means including a highly selective controlling circuit energized by the radio frequencyoutput taken from the plate circuit of the audio detector tube.

2. In combination with an amplifier having an output circuit resonant Vto an operating superaudible frequency, a detector having an input circuit coupled to said circuit resonant to said frequency, an amplifier for the audible frequency output of the detector, an automatic volume control circuit for said super-audible amplifier, said audio amplifier being normally maintained biased to cut-off whereby it is inefficient to amplify, a control network having a highly selective input circuit, resonant to said super-audible frequency, coupled to said first output circuit and being independent of said volume control circuit, the output of said network being connected to the audible frequency amplifier for reducing said bias and rendering the latter efficient to amplify Whenever energy of said super-audible frequency is impressed upon said super-audible frequency amplifier.

3. The combination, in a superheterodyne receiver, with a radio frequency amplifier resonant to an operating intermediate frequency, a detector, an audio frequency amplifier and an automatic volume control means for said radio frequency amplifier, of a control tube having a highly selective input circuit loosely coupled to the radio frequency amplifier, said input circuit being resonant to said frequency, an amplifier coupled to the output of the control tube, for normally maintaining an input electrode of the audio amplifier biased to cut-off, and a direct current connection between an output electrode of the amplifier for the control tubeoutput and said input electrode such that said cut-off bias is reduced when energy o-f said frequency is impressed on the radio amplifier. v

4. In 'a radio receiver, the combination of an Aaudio frequency amplifier, a network resonant to a desired operating frequency preceding the amplifier input, and coupled thereto, for providing an audio frequency signal to be amplified, said network including an automatic volume control circuit means for normally maintaining an input electrode of the amplifier biased to cut-off, and a control circuit connected between said electrode and a desired point in said network for sufficiently reducing the bias to render the amplifier conductive only when said signal is provided, said -control circuit including a highly selective input resonant to the said frequency but which is independent of said volume control circuit.

5. In a radio receiver provided with at least a high frequency signal amplifier, a demodulator of the diode type, a demodulated signal amplifier and a control arrangement, responsive to variations in signal intensity level, for adjusting the gain of said rst amplifier in such a manner that the signal input level to the demodulator is substantially constant, a second control arrangement, responsive to variations in the gain of said first amplifier, for rendering the said second amplifier inefncient when the gain of the first amplifier increases above a predetermined level, and said second control arrangement including a highly selective network resonant to an operating signal frequency and which is independent of said first control arrangement.

6. In a radio receiver provided with at least a high frequency signal amplier, a demodulator, a demodulated signal amplifier and a control arrangement, responsive to variations in signal intensity level, for adjusting the gain of said first amplifier in such a manner that the signal input level to the demodulator is substantially constant, a second control arrangement, including a rectifier coupled to said first amplifier for developing a control bias potential, for rendering the said second amplifier inefcient when the gain of the first amplifier increases above a predetermined level, and said second control arrangement including a. highly selective network resonant to an operating signal frequency and which is independent of said first control arrangement.

7. In an automatic volume control system for a radio receiver, said receiver including at least two successive high frequency amplifier stages, a detector, and at least one audio frequency amplifier stage, an automatic gain control network, responsive to variation in high frequency signal carrier intensity level, forl adjusting the sensitivity of the high frequency amplifier stages in such a manner as to maintain the signal input to the detector substantially constant, a second gain control arrangement having a resonant input network tuned to the frequency of the signal energy delivered to said detector, said resonant network being coupled to receive signal carrier energy from the output of said cascaded high frequency amplifiers, a means for connecting the second gain control arrangement to said audio stage in such a manner that the sensiintermediate frequency amplifier and the input electrodes of the detector, an arrangement for automatically,regulating the sensitivity of said audio amplier, `said arrangement including an electron discharge device having a resonant network connected between its input electrodes, said network being tuned to the operating intermediate frequency and including a connection to the primary of said transformer, and means including an electron discharge tube, for connecting an output electrode of said discharge device to an input electrode of said audio amplifier.

9. In a modulated carrier wave receiver, the combination with a carrier wave amplifier, a demodulator tube including at least a control grid, cathode and anode, and an audio frequency amplifier tube, an audio frequency signal coupling path connected between the demodulator tube and the said audio tube, means automaticallyto regulate the gain of said amplifier in response to received carrier Wave variations, a resistor operatively associated with the demodulator tube for developing a direct current voltage variable with said variations, an electron discharge tube having an input electrode connected to a point on said resistor, a resistor in the grid circuit of the audio amplifier tube and the anode circuit of said last tube, said point being so Vchosen that the gain of said audio tube is substantially decreased when received carrier waves decrease in amplitude below a predetermined level.

10. In a radio receiver of the type including a plurality of cascaded tubes, a network coupling at least two of the tubes, said network including a circuit tuned to a desired signal frequency, the first of said two tubes being a radio frequency signal amplifier, a noise suppressor system for the receiver comprising a control electron discharge tube provided with a resonant input network between its input electrodes, the last network being tuned to said desired frequency, means for coupling said last resonant network to said tuned circuit, a control amplifier tube having its input circuit connected to the output circuit of the control tube, and a resistor common to the output circuit of the last amplifier tube and the input circuit of the second of said two tubes.

11. In a radio receiver of the type including a plurality of cascaded tubes, a network coupling at least two of the tubes, said network including a circuit tuned to a desired signal frequency, the first of said two tubes being a radio frequency signal amplifier, a noise suppressor system for the receiver comprising a control electron discharge tube provided with a resonant input network between its input electrodes, the last network being tuned to said desired frequency, means for coupling said last resonant network to said tuned circuit, a control amplifier tube having its input circuit connected to the output circuit of the control tube, and a resistor common to the output circuit of the last amplifier tube and the input circuit of the second of said two tubes, and means operatively associated with at least one of said control and control amplifier tubes for adjusting the suppressor action.

12. In a radio receiver of the type including a plurality of cascaded tubes, a network coupling at least two of the tubes, said network including a circuit tuned to a desired signal frequency, the first of said two tubes being a radio frequency signal amplifier, a noise suppressor syst-em for the receiver comprising a control electron discharge tube provided with a resonant input network between its input electrodes, the last network being tuned to said desired frequency, means including a signal amplifier, for

coupling said last resonant network to said tuned circuit, a control amplier tube having its input circuit connected to the output circuit of the control tube, and a resistor common to the output circuit of the last vamplier tube and the input circuit of the second of said two tubes. I

13. In a radio receiver of the type including a tuned high frequency amplifier, a demodulator, an audio amplier network, automatic volume control means for regulating the gain of the tuned amplifier in a sense to maintain the signal'carrier amplitude at the demodulator input substantially constant over a range of signal carrier amplitude variations at the tuned amplifier input, a second control means, responsive to a decrease in the signal carrier amplitude below a desired intensity level, for impairing the demodulated signal transmission efficiency through said audio network, a third control means connected between the Volume control means and said second control means for rendering the latter operative to impair said demodulated signal transmission eiciency when the signal carrier amplitude increases above a desired intensity level.

14. In a radio receiving circuit, a selecting circuit, and an auxiliary circuit for rendering the set operative at frequencies immediately adjacent to and including the carrier frequency and at the same time rendering the set inoperative and silent when tuned over a substantial part of a given broadcasting channel, said auxiliary circuit comprising loosely coupled tuned circuits including audions, one of said audions having its control grid connected to said auxiliary circuit and its plate and an audio tube including a re'- sistor, connected through said audions to one of said tuned circuits through the medium of a coil and a detector tube, the plate of said second named audion being connected to the resistor of said audio tube.

15. Radio receiving apparatus of the type including a radio frequency automatic volume control arrangement, means for biasing a tube of the receiver to a. point where it is inoperative and apparatus for automatically removing such bias in the presence of a transmitted modulated carrier signal, which apparatus consists of means for diverting a part of a modulated carrier signal voltage to a highly selective tuned circuit for selectively relaying the modulated signal carrier tota vacuum tube operated as a rectifier, said tuned circuit being independent of said volume control arrangement, and means for applying the rectified voltage to modify the bias of the first mentioned tube to render it operative.

MADISON G. NICHOLSON, JR. 

